Duke Savora used to use the term "Sectional Density" in regards to this phenomenon. Basically making a point that, like a bullet, as the diameter of a bullet increases the weight behind it must increase accordingly to achieve the same penetration. Simplified it is the distribution of mass around the axis that focuses energy for penetration. If a quarter inch diameter arrow is in a state of yaw or flex the true orientation of the arrows mass could be an inch in diameter. Even more if distance is extremely close to the bow or the spine is light for weight. As the arrow stabilizes the yaw and/or flex is reduced improving the Sectional Density and ultimately penetration within the boundary of what energy has not been spent. Was always an interesting discussion when Duke explained his understanding of the art and science!
